MATLAB: How to vectorize a for-loop

for loopvectorize

Hello!
I would appreaciate any help vectorizing the for loop below. The problem i cannot solve is how to take out the constants from wdrive and multiply it with the rest, according to the loop below. I want to become better at vectorizing my MATLAB code so I would really appreciate any help! Thanks alot!
%S and R are square matrices (404*404).
%fc is a column vector
wdrive=0:1:800;
a2=zeros(2*dofs,(length(wdrive)));
b2=zeros(2*dofs,(length(wdrive)));
Amp=zeros(1,length(wdrive));
 SRS=S*(R\S);
SRfc=S*(R\fc);
for i=1:length(wdrive)
  a2(:,i)=(wdrive(i)^2*SRS+R)\(fs-wdrive(i)*SRfc);
  b2(:,i)=(R)\(fc+wdrive(i)*S*a2(:,i));
  Amp(i)=sqrt(a2(dofs-1,i)^2+b2(dofs-1,i)^2);
end

Best Answer

I don't think you can vectorize everything, but you can cut down on the operations done inside the loop,
     Rfc=R\fc;
     SRS=S*(R\S);
     SRfc=S*(Rfc);
     rhs=bsxfun(@minus,fs,SRfc*wdrive);
    for i=1:length(wdrive)
      a2(:,i)=(wdrive(i)^2*SRS+R)\rhs(:,i);
    end
     b2=Rfc+R\S*bsxfun(@times, wdrive, a2);
     Amp=abs(a2(dofs-1,:)+i*b2(dofs-1,:));
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